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Current Transformers General Info and Specs

Modified on: Wed, 3 Oct, 2018 at 10:26 AM

All of the current transformer models that we offer are compatible with any Omnimeter model. They are not compatible the 25IDS, 15IDS, or 15E models. Here is some universal data pertaining to the Current Transformers (CTs) that we offer:

Accuracy Class: 0.1%

26.6mA output. ——> So at 100A through it will output 13.3mA. At the full 200A it will output 26.6mA

CT output is AC

Our CTs have a Burden Resistance of 5 Ohms

200A CTs have 7500 internal windings.

When choosing a CT that will be best for your system consider these factors:

What is the outside diameter of your wire in millimeters? Order a CT that will fit on the wire (this is the most common ordering mistake). It is ok to oversize the CT (the wire passing through can be much smaller then the CT aperture) but if it is too small then you will need to replace the CT(s).

What is the amperage of your electrical system? Each CT has an amperage rating. Make sure that the CT model that you choose has an amperage rating the meets or exceeds your electrical system.

Do you want to use solid core CTs or split core CTs? Solid core CTs are cheaper, but require you to disconnect the primary wire, slip the CT over the wire, and then re-connect the primary wire. Split core CTs simply clamp around the primary wire in place.

Voltage varies widely depending on open circuit or not. These are not “voltage output” CTs, but rather amperage output.

We carry many sizes of CTs, as well as solid and split core options.Our CTs come with 6 foot leads. We do not recommend that you extend the length of the CT wires (because of loss of accuracy). But if you have to, be sure to solder and use shrink tubing on the connections. CTs with extended wire length lose about 1% accuracy every 50'. We cannot certify accuracy when you do this. It is ideal to locate the meter and CTs at the power system you are monitoring and then you can go long distance with the communication – USB, iSerial, Push, etc.We have CTs that can meter up to 5000 amps in stock. The CT ratio is selectable inside the meter. Here is our selection of CTs:Current Transformers

Our CTs are not the common 5A output CTs. They are optimized for accuracy and small size. They are much higher quality than 5A output CTs. The reason is that phase angle characteristics improve as the number of turns increases, but amperage output decreases as number of turns increase. So we have chosen what we consider to be an optimal output of 26.6mA.

If you have to disconnect a CT from the meter and leave the CT installed on the primary wire, be sure to short the secondary wires together. A CT can be damaged if it is left on a primary wire carrying a lot of amps without having the secondary wires shorted to each other.For choosing the best CTs for your Omnimeter you will need to know your wire size diameter and if you want to use Solid-Core or Split-Core. Solid-Core are less expensive but are a bit more difficult to install, they require that you disconnect the wires being read and slip the CT over the wire. Split-Core CTs are more expensive but they very easily just snap around the wires being read.

Use 1 CT for single phase 2-wire systems (one hot (110V to 415V) and one neutral, with or without ground).

Use 1 CT for 2-wire systems (two hot wires (110V to 240V) and no neutral)

Use 2 CTs for a 120/240V three-wire system (two hots and a neutral, with or without ground).

Use 2 CTs for 3-phase 3-wire systems. (without neutral, up to 415V)

Use 3 CTs for 3-phase 4-wire systems. (with neutral, up to 480V)

For UL Listed Omnimeters:

Use 1 CT for single phase 2-wire systems (one hot (110V to120V) and one neutral, with or without ground).

Use 2 CTs for a 120/240V three-wire system (two hots and a neutral, with or without ground).

Use 2 CTs for 3-phase 3-wire systems. (UL Listed up to 240V, up to 415V is possible)

Use 3 CTs for 3-phase 4-wire systems. (UL Listed up to 240V, up to 480V is possible)

Important note on CTs:

CT's can be damaged if energized and open-circuited. So the safe way to deal with them is to either de-energize the main circuit while you’re doing the install, (most preferred), or connect them to the meter first, then install them around the main wire, (also OK), or short the black and white CT wires while you install, and then, assuming there’s substantially less than their rated current running through them, connect them as quickly as possible to the meter (least preferred). The inducted current in the CT will damage the CT if it has a chance to build up heat in the internal coils, which can happen if there is no resistance across the 2 leads (open-circuit). Shorting the CT wires when they are not connected to a meter is not a problem. Leaving them un-shorted and not connected to a meter is the problem.